A global analysis of $b\to s\ell \ell$ data in heavy and light $Z^{\prime }$ models

Abstract

We perform a model-independent global fit to all $b\to s\ell \ell$ data in the light of recent measurements of the lepton flavour universality violating (LFUV) observables $R_{K_S^0}$ and $R_{K^{\ast +}}$ as well as the updated measurements of observables in $B_s\to \varphi {\mu }^{+}{\mu }^{-}$ decay, by the LHCb collaboration. We obtain new physics (NP) solutions to the current anomalies in the data, assuming NP in the muon sector only. We find that the 1D NP scenarios $C_9^{\mathrm{NP}}<0$ and $C_9^{\mathrm{NP}}=-C_{10}^{\mathrm{NP}}$ continue to be the most favoured ones. However, the significance of the then favoured scenario $C_9^{\mathrm{NP}}=-C_9^{\prime }$ has reduced and the updated data now marginally prefers $C_{10}^{\mathrm{NP}}$ scenario over $C_9^{\mathrm{NP}}=-C_9^{\prime }$. The 2D scenarios $(C_9^{\mathrm{NP}},C_{10}^{\prime })$, $(C_9^{\mathrm{NP}},C_9^{\prime })$ and $(C_9^{\mathrm{NP}},C_{10}^{\mathrm{NP}})$, continue to be favoured by the data in the listed order. We also analyse generic TeV scale $Z^{\prime }$ models which can generate the favored 1D scenarios, $C_9^{\mathrm{NP}}$ and $C_9^{\mathrm{NP}}=-C_{10}^{\mathrm{NP}}$ along with the 2D NP scenarios $(C_9^{\mathrm{NP}},C_9^{\prime })$ and $(C_9^{\mathrm{NP}},C_{10}^{\mathrm{NP}})$. Using the additional constraints from $B_s-\overline{B_s}$ mixing and neutrino trident data, we find that all four models provide an equally good fit to the data. Further, we consider a model with a 25 MeV $Z^{\prime }$ that couples to muons and has a $q^2$ dependent $b-s$ coupling. We also study the implications of the current data on the LFUV observable $R_{\varphi }$, $Q_{4,5}$ along with $R_{K^{(\ast )}}$ in the high $q^2$. We find that a precise measurements of these observables can provide a good discrimination between a few favored model-independent solutions, and have a potential to disentangle different heavy and light $Z^{\prime }$ scenarios considered in this work.

Comments: 25 pages, 3 figures; Published version